Organic azo pigments are well known in the art and are particularly useful as coloring components in various types of printing inks, paints and plastics. Azo pigments are characterized as containing one or more azo groups (i.e., --N.dbd.N--). Azo pigments are prepared from various aromatic amines by a two-step process involving diazotization and coupling. The choice of amine is determined by the color and properties of the dye prepared from the amine, the cost of the amine, the ease of diazotization, stability of the diazonium salt, etc.
Diazotization involves treating a primary aryl amine with nitrous acid to form a diazonium salt. The diazonium salt is then reacted with a coupling agent to form the azo pigment. Coupling agents used to prepare azo pigments contain an active hydrogen atom bound to a carbon atom, and examples of types of compounds which have been used as azo coupling agents include compounds containing a phenolic hydroxyl group such as phenols and naphthols, aromatic amines, compounds that contain enolyzable ketone groups of an aliphatic character and some heterocyclic compounds such as those containing pyrrole, indole, and similar ring systems.
Azo pigments may be subdivided chemically according to the number of azo groups present in the pigment such as monoazo, disazo, trisazo, tetrakisazo, etc. Diaryl pigments containing coupled mixed bis-diazotized diamines and acid-substituted aromatic amines are described in U.S. Pat. No. 4,968,352. The pigments are obtained by coupling a bis-diazotized-substituted benzidine and a diazotized primary aromatic acid amine as well as mixtures of such amines with acetoacetanilides or with pyrazolinones. Generally, the amount of the aromatic acid amine employed ranges from about 0.25 to about 15% by weight of the final pigment, and preferably, the acid amine is used at a level of about 0.1 to about 15 mole percent based on the moles of the acetoacetanilide coupler. The pigments may be prepared by diazotizing a mixture of the benzidine and the aromatic acid amine and thereafter coupling the diazotized mixture.
U.S. Pat. No. 4,251,441 describes pigments of mixtures of methoxynitrobenzene-azo-methoxy acetanilides. The mixtures are prepared by diazotizing a mixture of 5-nitro-2-amino-anisol and 3-nitro-4-amino-anisol and thereafter coupling the diazotized mixture with acetoacetic acid-o-anisidide. The anisol mixture may contain from 75 to 85% by weight of the 5-nitro derivative and from 15 to 25% of the 3-nitro derivative. The mixtures obtained are reported to be characterized by a high tinctorial strength, a high gloss, good transparency and good rheological properties.
U.S. Pat. No. 4,602,960 describes modified diarylide pigments. The pigments contain (a) a pigment which is composed of a tetrazotized benzidine coupled to an acetoacetarylide and/or a 1-phenyl-3-methyl pyrazole-5-one, and (b) a water-soluble component obtained from a symmetric or asymmetric coupling product of a tetrazotized 4,4'-diamino-2,2'-stilbene disulfonic acid and an acetoacetarylide and/or a 1-phenyl-3-methyl-5-pyrazollone.
U.S. Pat. No. 4,885,033 describes pigments based on acetoacetarylide derivatives. The pigment composition which is suitable for use in modern offset and letter press inks comprises the mixture of
(A) (a) a pigment which may be derived from a mixed coupling of two or more coupling agents and tetrazotized (or bis-diazo) 3,3'-dichlorobenzidine, (b) a dyestuff derived from specified coupling agents onto tetrazotized benzidine-2,2'-disulfonic acid; and optionally (c) a resin; and PA1 (B) (a) a pigment derived from one or more specified coupling agents onto one or both of tetrazotized 3,3'-dichlorobenzidine and tetrazotized 3,3'-dimethoxybenzidine and (b) an aliphatic amine. PA1 (A) a mixture comprising from about 5 to about 95% by weight of each of two or more diazonium components derived from aromatic amines provided that: PA1 (A-1) if one of the aromatic amines in the mixture contains a carboxamide group, then the other amine in the mixture is a diaryldiamine; or PA1 (A-2) the mixture comprises about 20 to about 80% of each diazonium component when one of the aromatic amines contains a carboxylic acid, sulfonic acid, or salt thereof, and the other aromatic amine is a diaryldiamine; or PA1 (A-3) the mixture comprises from about 30 to about 70% of each of the diazonium components when the aromatic amines in the mixture contain a nitro group; and PA1 (B) an organic coupling component, provided that when the coupling component is a 2-naphthol characterized by the formula ##STR1## wherein R.sup.1 is hydrogen or --COOH, the mixture (A) may comprise from about 5 to about 95% by weight of each of two or more diazonium components derived from aromatic amines containing carboxamide groups, and the mixture does not have to contain a diaryldiamine.
The ratio of components (A) and (B) in the pigment composition ranges from 35:65 to 95:5. The dyestuff of (B) (a) may include mixed coupled azo pigments prepared from one or more coupling agents with one or two tetrazotized dichloro or dimethoxybenzidines.
Various types of mixed coupled azo pigments are described in Vol. 4, pp. 1510-12 of the Colour Index, Third Edition, Revision 1982, Additions and Amendments No. 62, January 1987, Published by the Society of Dyers and Colourists. In particular, two types of "mixed couplings" are described. In the case of yellow pigments, each is described as a product of the reaction between a tetrazotized diamine (D) (i.e., a bis-diazo component) and two coupling components (E) and (E'). Such reactions are reported to produce three definite compounds, i.e., E-D-E, E'-D-E' and E-D-E'. Specific examples of such yellow pigments identified in the color index are C.I. pigment yellow 114, C.I. pigment yellow 126, C.I. pigment yellow 127 and C.I. pigment yellow 176 at page 1512. Red pigments which are "mixed couplings" are described as formed by reaction of one amine (A) and two coupling components (E) and (E'). Such coupling reactions produce a mixture of two components, i.e., A-E and A-E' in proportions defined by the concentrations of (E) and (E') in the reaction mixture. It is reported that these reactions in situ can produce synergistic effects not obtained by physical admixture of the two components. C.I. pigment red 184 and C.I. pigment red 210 are examples of such mixed couplings found at page 1511.
Czech Patent 235,634 describes a pigment which is prepared through the coupling of a mixture of diazotized p-amino acetanilide and p-aminobenzamide with 2-hydroxy-3-naphthoyl-o-anisidide. The Czech patent describes in Example 1, that the coupling is completed by heating to 60.degree. C. and adding an aqueous solution containing 6 grams of potassium colophony followed by 3 grams of calcium chloride. The colophony or calcium colophony is included in the pigments apparently to provide improved properties.